What does dilatancy mean?
Dilatancy names the tendency of a material to increase in volume when it is deformed by shear. The effect is especially important in densely packed granular materials such as sand: when the material is disturbed or sheared, its particles tend to rearrange into a less compact structure, causing a measurable increase in bulk volume. This behavior is important in geotechnical engineering because it affects shear strength, foundation stability, slope performance, and the movement of soil around underground structures. Engineers may measure a material's angle of dilatancy to describe the relationship between shear stress and volume change. Although dilatancy occurs more broadly in the mechanics of granular and porous materials, it is not usually used in everyday speech. The term should not be confused with dilation in general, which can refer to any widening or expansion; dilatancy specifically identifies expansion associated with shearing.
nounDilatancy is the property of a material, especially densely packed soil or another granular substance, of increasing in volume when subjected to shear stress.
- The tendency of a material, especially a densely packed granular material such as soil, to increase in volume when subjected to shear stress.
"Engineers accounted for the soil's dilatancy when calculating the likely movement of the foundation."
"The densely packed sand showed pronounced dilatancy as the test imposed increasing shear stress."
"The geotechnical model included an angle of dilatancy estimated from laboratory tests."
The plural is grammatical but rarely needed, because the property is often discussed collectively or in the singular.
"The researchers compared the dilatancies of several different soil samples."
Why does disturbed sand sometimes become bulkier? Dilatancy is the answer: shearing tightly packed granular material can make it expand.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does dilatancy come from?
Dilatancy was formed in English during the 19th century from the stem of dilatation and the suffix -ancy. Its ultimate source is the Latin verb dilatare, meaning “to widen” or “enlarge.” The same Latin root produced related English words including dilate, dilatation, dilatant, and dilator.
How dilatancy is actually used
This is a specialized term used chiefly in soil mechanics, geotechnical engineering, and the mechanics of granular materials. It is uncommon in general prose.
Easily confused with dilatancy
Dilation is the general process of widening or expanding, whereas dilatancy specifically denotes an increase in volume caused by shear.